Automatic irrigation sprinkler systems have been devised to supplement, or substitute for, natural rainfall in maintaining grasses, flowers, shrubbery, and trees on lawns, golf courses, parks, cemeteries, and the like. In times past, automatic irrigation sprinkler controllers were electromechanical devices which cycled water to various watering zones within the system using electrically driven program wheels having pins and cams which engaged mechanical switches to energize solenoid driven zone valves. Such electromechanical controllers were generally effective and reliable, but mechanically complex and, thus, expensive to manufacture and maintain.
In time, electromechanical irrigation controllers have been supplemented, and eventually supplanted by, analog and digital circuitry. At present, irrigation controllers are almost exclusively digital with programmed microprocessors or microcontrollers operating through solid state power switches, such as triacs. In order to provide the required controlling features, modern digital controllers have, in a sense, replaced mechanical complexity with program and logical complexity. Modern digital irrigation controllers often have complex arrays of displays and programming switches which can be confusing and laborious to understand and operate. Such controllers are often installed in locations where it is not convenient or comfortable to stand, with operating manual in hand, and attempt to program. While large facilities, such as golf courses, can afford to hire consultants and staff capable of programming and adjusting the programs of digital controllers, such outside expertise is often not available to individual homeowners, at least not economically.
Another problem with both older electromechanical controllers and many digital controllers is that they are configured to control a limited number of watering zones. If additional watering zones are needed, a more expensive model with a greater number of controllable zones must be purchased. At least one digital controller is known which has the capability of expanding the number of controlled zones. However, the manner of expansion is by connecting an external expansion module to the existing cabinet by way of an externally accessible connector. In some circumstances, installing an external module on the existing controller cabinet is difficult, if not impossible. Additionally, there are concerns about the reliability of an externally connected module.